In simple terms yes, if you upgraded to 1.3 via PC you have the phone in a brand-new-updated state. The backup you did just before upgrading contains every info to restore the apps you used before, so you have to confirm and let the N900 to redownload and reinstall all the old apps for you, and then everything should be fine. It could work not 100% for 'special settings' - let's say if you stay on tracks and don't use extras-testing and extras-devel repositories you are safe, otherwise you have to start to know a little bit more about your N900 .

after 1.3 I can't download some files on Ovistore (themes, wallpapers)

Actually, for my understanding, that was Nokia N900 software version 20.2010.36-2, not PR1.3?! Is that true?

It is PR1.3. You can read here:
http://en.wikipedia.org/wiki/Maemo

Latest stable release 5.0 PR1.3 / 25 October 2010; 0 days ago

20.2010.36-2
October 25 2010
PR1.3,
Qt 4.7.0, Full OVI-Suite support, updated kernel with kexec patches for MeeGo, bug fixes.

lol at quoting wikipedia as a reliable source of information, you do realize that anyone can put anything on wikipedia right? the edits are even done by someone from the USA, so in all likelyhood not by someone at nokia

same here.My contacts list is empty.App himself shown on desktop.
I reinstalled and installed but no changes.
Does somebody had luck and somehow successfully get list back?

Before up-dating, the device will ask you to make a back-up. Did u make 1 ?? ( Hope u did )

)ust a thought, most of the screw ups seem to be user issues rather than software or hardware. Is there anyway to keep the update instructions on the active topics of the forum during the duration of maemo update (bout a week or so) to help out the noobs?
Thanks.

First, some of N900 users live in the USA, so someone from the USA can know something about Maemo .
Second, if the quotes from Wikipedia weren't true, they would be deleted from the article quickly, by anybody who would know that the information isn't true.
Encyclopedia looks like a reliable source of information, even if it is Wikipedia.

Here is how I have just updated.
1. set up USB Networking (I don't want to flash and erase all the information), with Ubuntu, as I'm too lazy to set it up with Windows;
Read N900 USB Networking in wiki.
http://wiki.maemo.org/N900_USB_networking
1.1. type "ifup usb0"; it should say "already configured";
1.2. type "ping 192.168.2.15"; if it cannot ping, type "ifconfig usb0 192.168.2.15";
1.3. type "ping <some local IP of your LAN>"; if it cannot ping, type "route add default gw 192.168.2.14";
1.4. type "ping google.com"; if it cannot ping, check that your LAN can ping google.com.
1.5 try to set up a dummy network; browser can see the web, Dummy is listed in Internet Connections in Settings, but HAM still cannot see the web because Dummy isn't in the list of suggested connections;
2. apt-get update;
3. apt-get upgrade;
4. apt-get install mp-fremantle-generic-pr;
5. by now you have run out of space, haven't you?
6. apt-get autoremove, apt-get clean, df -h /;
7. try "apt-get -f install mp-fremantle-generic-pr" or something else, don't remember exactly;
8. Success: you can see this line:
Setting up mp-fremantle-generic-pr (20.2010.36-2)
9. Reboot to see new version in About.
10. Contacts and most settings and installed application are intact. Except transitions.ini and unlocked FM transmitter.
If /etc/mce/mce.ini (including LED patterns) was modified, you would be asked whether you want to update it or not; you can make a backup and then update it to the new version (as you don't have diff, you cannot see the differences between your and new versions).
I don't see much immideate improvements; I'm going to change transitions.ini again and return LED patterns.

I'm glad that the update improves battery life and speed in general.
There are about fifty bugs fixed?

there may be 50 bugs (so they claim) corrected ...but i would guess there are about 100 more bugs created by this update..this update is a disgrace.